Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
777 FXUS66 KSGX 231021 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 320 AM PDT Sun Jun 23 2024 .SYNOPSIS... Warm near the coast today and hot again in the valleys, mountains and deserts. A moisture surge will bring higher humidity and a slight chance of showers and thunderstorms, primarily over the mountains and deserts. High heat will continue in the deserts through Thursday where an Excessive Heat Warnings is in effect. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Skies were clear early this morning over the coastal zones and also over the coastal waters west of San Diego. Low clouds and fog were north over the Los Angeles and Ventura county coastlines. This vanquished marine layer clouds over coastal San Diego and Orange Counties will result in the few degrees of warming in these areas today compared to yesterday. Valley highs Saturday topped out at 99 at Yorba Linda, 100 at Ramona, 102 at Ontario, and 106 at San Bernardino and March ARB. Hot again in the valleys today where a Heat Advisory remain in effect through 8 PM. Desert highs Saturday reached 100 at Victorville, 102 at Apple Valley and Johnson Valley, 110 at Palm Springs and 111 at Ocotillo Wells. Excessive Heat Warnings are in effect for the deserts through Thursday as a ridge of high pressure centered over the Four Corners keeps the heat dome over the desert Southwest through the middle of the week. An overnight low level moisture surge into the lower deserts raised surface dewpoints from the mid 50s into the upper 60s and low 70s at Thermal, Indio, and Palm Desert. Mid-level moisture was streaming into SoCal from the southeast. Satellite imagery showed midlevel clouds over northern Baja and western Arizona. The chances of showers over the coastal waters, the coastal zones and most of the inland valley has been lowered. At 3 AM, the closest radar returns were over north central Baja and were moving northeast toward Sonora, MX. PWAT`s peak this afternoon over the lower deserts at 1.75" and around 1.10" over the mountains, but the high resolution SPC HREF models only show isolated convection over the mountains and deserts this afternoon. The HRRR follows a similar trend and shows isolated afternoon convection over the mountains. The 00Z WRF is dry. Given this downward trend in the chances for convection, the chances for thunderstorms over the coastal waters and most of the coastal and valley zones are too low to include in the forecast. Afternoon chances for t-storms on Monday will also be low with the best chance for convection over the San Bernardino Mountains. Temperatures west of the mountains will fall a couple degrees each day Monday through Thursday as a Pacific trough weakens the ridge, slowly lowers heights, and slowly increases the marine layer depth. && .AVIATION... 230910Z...Coast/Valleys...SCT to locally BKN low clouds with bases 700-1000 ft MSL near the immediate coast through 17Z. Chance of a CIGs at coastal TAF sites is less than 30 percent. Tops will be 1200 ft MSL, with local VIS 3-5 miles on higher coastal terrain. There is a less than 10 percent chance of TS 18Z to 02Z Mon. Otherwise, SCT- BKN clouds mostly at/above 9000 ft MSL through this evening. Mountains/Deserts...There is a 20-30 percent chance of TSRA between 17Z and 04Z Mon, with CB tops to 35000 ft MSL and possible strong up/downdrafts and local surface wind gusts over 30 kt. Otherwise, SCT-BKN clouds mostly at/above 9000 ft MSL through this evening. Local west winds with gusts 25-35 kt will develop after 22Z, continuing this evening on the desert mountain slopes and into the deserts and the San Gorgonio Pass. && .MARINE... No hazardous marine conditions are expected through Thursday. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...Heat Advisory until 8 PM PDT this evening for Orange County Inland Areas-San Bernardino and Riverside County Valleys- The Inland Empire-San Diego County Valleys. Excessive Heat Warning until 8 PM PDT Thursday for Apple and Lucerne Valleys-Coachella Valley-San Diego County Deserts- San Gorgonio Pass Near Banning. PZ...None. && $$ PUBLIC...Moede AVIATION/MARINE...PG